In installations used for coating flexible substrates, typically a web of a synthetic or polymeric film and herein also referred to as web-form material, a first web drum is unwound, the wound-off web-form material is coated, for example by sputtering, chemical vaporization deposition (CVD) and wound up again on a second web drum. The aforementioned first and/or second web drums may be replaced with new and full web drums and/or empty web drums whenever necessary. The term web drum is also referred to herein as web module.
In known arrangements and methods for coating a web-form material, the steps of winding up and unwinding the web-form material are conducted in winding up and unwinding chambers, typically separated from the one or more coating sites. Further, the web-form material may be directed over a multitude of guiding or re-directing rollers when travelling from the unwinding drum, over the coating site, which may be in a separate processing chamber, to the winding up drum.
Typically, flexible web-form materials such as, for example, polymeric web substrates may charge electrically on winding and/or unwinding due to frictional contact-induced charge separation. Generally, charge generation may occur on web-form materials, especially, when they rub, slide or separate from other surfaces during processing. Often, the more rapidly this occurs the greater are the amounts of charges likely to be generated. Hence, depending on the type of coating, typical, installations for coating web-form substrates may move the web-form material at low speeds of, for example, 0.1 to 25 m/min or 0.2 to 50 m/min, or at high speeds of, for example, 10 to 20 m/s or more. Further, charge accumulation may occur since the web-form substrates often consist of polymeric materials with high surface resistivity. Furthermore, since web-form substrates often travel long distances inside a processing installation, for example, during a coating process charge leakage from the web-form substrate to earth may be restricted.
In general, enhanced installation design may reduce electrostatic charge on a substrate, for example by ensuring adequate earth grounding of all metal parts of the equipment so that dangerous quantities of electrical charge may be prevented from accumulating. Further, the mechanical handling of flexible web-form substrates may be designed, for example to minimize sliding on stalled rolls. Furthermore, antistatic coatings may be used for processing a flexible web-form substrate.
Nevertheless, in most instances during processing, the web-form substrate is unavoidably in frictional contact with more than one substrate handling device (e.g. guide or re-directing rollers) or unwound resulting in the presence of static charges on the web-form surfaces. It follows that static charge levels in the range of ten's of kV may be present on the surfaces of web-form materials during processing. These charges may electrostatically attract unwanted particles to the surfaces of the web-form material, for example, particles generated in the process and/or winding/unwinding chambers. Further, for instance, particles of silicon oxides generated in the winding/unwinding modules due to outgas sing of the web-form material may adhere onto the electrostatically charged surfaces of the web-form material. Furthermore, particles from the processing gas, for instance silane particles may flow from the one or more coating sites to the winding/unwinding modules during processing.
Such unwanted particle accumulation on the surfaces of the web-form material may lead to the destruction of the product. For instance, unwanted particles that adhere to the surface of the web-form material before coating, e.g., in-between the unwinding module and coating site may cause arcing during the coating process leading to web cutting and ultimately to the destruction and loss of the product. Further, defects at the web surface such as scratching may result from unwanted particles adhering to the surface of the web-form material, e.g., in-between the coating site and winding module.
In other instances, for example, the accumulation of unwanted particles may disrupt the homogeneity of the thin-film that is deposited on the web-form material during a coating process such as, for example, during sputtering. Furthermore, measurements of web thickness by, for instance, gauging systems may be distorted by the accumulation of unwanted particles on the surfaces of the web-form material. Such distortions may then compromise product changeover times, roll quality, product uniformity or shift repeatability.
The aforementioned damaging effects to the web-form material may be multiplied if the web-form material is exposed to the coating process more than once, i.e. when a surface of the web-form substrate is exposed to multiple coating steps. It follows that the costs incurred due to product loss through contamination with unwanted particles adhering to the surface of web-form materials before and after the coating process may be substantial.
For this purpose, it will be appreciated that systems and methods to significantly reduce or eliminate unwanted particle contamination on web-form materials before and/or after the coating process are desired. Hence, the subject matter described herein pertains to such methods and systems that reduce or eliminate unwanted particle accumulation on the surfaces of web-form materials.